Progress towards understanding mammalian olfactory coding has been hindered by: 1) our inability to identify receptors that make a measurable impact on odor perception and 2) the highly complex and distributed nature of higher order olfactory projections in the brain. Volatile odorants are detected by a large family o olfactory receptor genes in the mouse. This includes two families of canonical odorant receptors (ORs) containing over 1,000 members, and a small family of 14 Trace Amine-Associated Receptors (TAARs). We have shown that the TAARs play a critical role in the detection of amines-a class of compounds that elicits avoidance behavior in nave (untrained) mice. Moreover, the TAARs are required for the aversive quality of the amines. Because a majority of TAARs project to a cluster of glomeruli in the dorsal olfactory bulb, the neural circuitry underlying amine aversion can be traced from a genetically identifiable starting point. Here I propose to identify projections from TAAR glomeruli to higher brain regions, and to define their functions in odor processing. Specific Aim 1 will map the projections of olfactory bulb output neurons that get input from the TAAR glomeruli. Specific Aim 2 will optogenetically silence TAAR specific input to individual olfactory regions in order to determine their role in amine detection and aversion. Achieving these aims will be a key first step in identifying higher order neural circuitry that contributes to odor valence and olfactory perception in mammals.